Electrochemical gas separation devices based on oxygen ion-conducting solid electrolytes have practical applications in the production of high-purity oxygen from air and in the removal of residual oxygen from inert gases such as argon and nitrogen. These devices typically comprise multiple electrochemical cells, each of which is fabricated with multiple layers or components including an electrolyte layer, anode and cathode layers in contact with the electrolyte layer, and interconnect layers in contact with the anode and cathode. The multiple-cell devices may be fabricated into modules designed for the introduction of feed gas into the cells and the withdrawal of permeate and non-permeate gas from the cells.
In these applications, the separation device may be operated with a difference in gas pressure and/or gas composition between the feed (cathode) sides and the product or permeate (anode) sides of the electrolyte layers. The strength of the components in the separation device and the stability of the required gas-tight seals between the layers must be sufficient to sustain practical pressure and/or composition differentials over the economic operating lifetime of the device.
Separation devices based on oxygen ion-conducting solid electrolytes can be constructed in tubular, flat plate, or honeycomb configurations. The flat plate configuration, in which a plurality of planar electrolyte cells are stacked to operate in electrical series, is favored in many applications for ease of assembly, cost effectiveness, and compact dimensions. Any configuration, however, must be designed with appropriate component strength and seal integrity to operate at a pressure differential between the feed and product gas streams while maintaining purity requirements of the product gas streams. Higher efficiency may-be obtained by minimizing resistances in the cell including ohmic (electrolyte) and non-ohmic (electrode) resistances. Electrode resistance typically is a function of the choice of electrode material, the surface area of the electrode material, and the method of contact or bonding between the electrode and electrolyte layers. Low electrode resistance may be achieved with mixed conductor electrodes, high electrode surface area, and high open porosity in order to achieve low gas phase polarization and strong bonding with the electrolyte. Low electrolyte resistance is dependent on high ionic conduction and a short path length. For this reason, thin electrolytes are desired. Lower resistance leads to lower specific power, which in turns lowers the joule heating and associated thermal stresses on the device.
The design and fabrication methods for these electrochemical devices should provide operating systems with low resistance, thin electrolytes with high mechanical strength, and robust gas-tight seals to maintain gas pressure differentials between the anode and cathode sides of the cells and to ensure the required purity of the product gas streams. In order to meet these requirements, improved methods for the design and fabrication of these devices are needed in the field of electrochemical gas separation. The embodiments of the present invention meet these needs by providing improved design and fabrication methods as described below and defined by the claims that follow.